Wireless local area networks (WLANs) are becoming popular communications systems, in addition to being convenient data networking systems. Specifically, manufacturers are working to develop WLANs as telephony systems as an alternate to wide area cellular systems under certain circumstances, such as business and other enterprise organizations. Providing telephony service over WLANs allows a relatively inexpensive alternative to traditional wireless cellular communication. An organization can set up a WLAN, allowing authorized communication devices to access telephony service over the WLAN.
As with cellular telephony and mobile communication systems, users of WLAN telephony services will be mobile, and as they move through an area served by a WLAN system, their WLAN mobile station will occasionally have to handoff service from one access point to another. To prevent unauthorized access to telephony services, WLAN standards such as IEEE 802.11i provide security for authenticated handovers. A method specified in IEEE 802.11i uses a 4-way handshake process. When a mobile station needs to handover from a presently associated access point to a neighboring access point, the mobile station first transmits a reassociation request to the neighbor access point, including a pairwise master key identifier (PMKID). The neighbor or target access point transmits a reassociation response, which is followed by an acknowledgement by the mobile station. The target access point then transmits the first handshake message including a pseudorandom value known as an ANonce. The mobile station then responds by transmitting a pseudorandom value it has generated known as the SNonce, as well as a message integrity code, and other security related information. Two additional exchanged take place until the target point and the mobile station are both in possession of a common session key, each having generated the session key. Once the session key is acquired by both the mobile station and the target access point, the session key is installed at each station and secure communication commences using the session key for security. This process typically takes 800-1000 milliseconds in the case where the neighbor access point and the mobile station must acquire the PMK from an authentication server prior to executing the 4-way handshake. It is desirable to reduce the time it takes to handover, therefore there is a need to reduce the handover time, while still providing security comparable to that provided by present systems.